1. Field of the Invention
This invention relates to a method and apparatus for producing a solid braid structure and to a structure produced by said method and apparatus.
2. Description of the Prior Art
Braided structures are increasingly being used in industry to provide strong, lightweight and non-metallic components. Particular industries requiring such braided structures are the automobile industry and the aircraft industry. The advantage of a braided structure is that the structure has good tensile strength in all directions as opposed to a woven structure which has a relatively limited tensile strength in directions other than those in the direction of the weft and the warp of the yarns comprising the structure.
In order to fit in with industrial requirements, there is a need to provide braid structures in a complex form. By a complex form it is intended herein to refer to a form with a cross-section other than that of a simple rectangule or tube, or a moderate variation therefrom. Typical complex forms which are required are forms having, for example, I, J or C cross-sections. Attempts to form such cross-sections in a braiding apparatus have previously not been particularly successful since, at any area where there is a re-entrant portion, the yarns of the braid tend to span the entrance and therefore defeat the form being sought after.
In other complex forms of structure which do not have re-entrant portions, such as ones sought to have relatively sharp corners or edges, there is a tendency for the braid as laid to be unduly tensioned over the corner or edge and for the braid to open so that the braided structure does not have a uniform strength throughout.
Braided structures are usually of two forms, either those created in a flat form where a braided apparatus has plurality of serpentine tracks and package carriers of yarn travel the tracks interbraiding the yarn dispensed by carriers. At the ends of the paths the carriers are reversed in their direction. If flat multilayer braided structures are required, then a number of layers have to be assembled together and interstitched.
A braid of a generally tubular cross-section, e.g. circular, is able to be made by braiding apparatus in which serpentine paths are defined in a ring and the braid is formed in an area of access of the ring. The package carriers of yarn continuously traverse round the serpentine paths of the ring to lay down the tubular braid as it progresses through the apparatus.
The braid may be formed over a mandrel and this may be of a cross-section other than circular to a limited degree.
Multilayer braided structures have been proposed where radial yarns project from a mandrel and the package carriers of yarn weave their yarn around the radial yarns. Such structures have been difficult to manufacture and a novel and improved method and apparatus for constructing a multilayer braid of flat or hollow form where the various layers are interwoven one with the other during the manufacturing process is described in pending U.S. patent application Ser. No. 501,043 now abandoned. The present invention develops the idea of the multilayer structure described in that Patent Application.
One proposal which has been made previously to form complex braid structures is that the structure should be developed as a series of components which are then joined together. As a C a structure can effectively be constituted of three simple straight structures which are joined at the corners for example by stitching or enveloping in a woven sleeve, the whole can be impregnated if necessary to make a composite braided structure.
Where mandrels are used to create braided structures and a whole range of structures are required there is a disadvantage that a different type of mandrel is required for each size or variation of shape. While this considerably increases tooling and production costs and it is obviously advantageous if the range of mandrels required can be substantially reduced in size or eliminated.
It is thus desirable to seek ways of producing a wide range of braided complex forms, as well as simple forms, in a cost effective manner and in a manner which does not require complex or expensive apparatus and in which the apparatus is able to be adapted swiftly from the manufacture of one complex form to another.